(1) Technical Field
The present invention relates to a Raman probe connecting an excitation light source, a Raman spectrograph and a sample, and a Raman spectrum measuring apparatus utilizing the Raman probe.
(2) Background Art
In recent years, there is a growing need for the development of non-invasive medical diagnostic techniques that are more objective and more quantitative. As a result, high expectations are placed on spectroscopic technologies, for example in connection with the diagnosis and treatment of arterial sclerosis. A vascular endoscope has recently been developed for the diagnosis of arterial sclerosis. This endoscope, however, is only capable of observing the color and form of an affected part, and it is not suitable for quantitative observation or definite diagnosis of the progress of the symptom. In the nidus of sclerosis, various lipids, such as cholesterol ester, are accumulated, and it is expected that the progress of arterial sclerosis can be diagnosed by analyzing the amount of accumulated lipids and the ratio of components. For this diagnosis, Raman spectroscopic analysis has been proposed as a highly objective definite diagnosing method. Based on the determination of the fingerprint region of lipids and the CH rolling vibration mode (˜3000 cm−1), the ratio of cholesterol to the entire amount of lipids can be analyzed. Expectations are placed on diagnosis based on spectrum analysis using a Raman scattering measuring extra-fine fiber probe that is capable of being introduced into blood vessels.
When measuring Raman scattering of a sample in situ, for example, excitation light is guided by means of a Raman probe to a measured portion of the sample, and signal light from the sample is guided via the probe to a Raman spectrograph. However, optical fibers, such as a quartz fiber, that are used as the Raman probe themselves generate Raman scattered light. Raman scattered light is also generated by the optical fiber on the exciting end as well as one on the receiving end. Raman scattered light from the excitation-side optical fiber is shone onto the sample together with the excitation light, and as it enters the receiving optical fiber, it interferes with the Raman scattered light generated from the sample. Further, if the excitation light with which the sample has been irradiated is reflected or scattered by the sample and is then incident on the receiving optical fiber, Raman scattering is caused in the receiving optical fiber as a result, which would also interfere with the measuring of the Raman scattered light generated from the sample.
These interfering light not only lower the S/N of the measurement signal, but could even make it impossible to perform measurement if the signal from the sample is very weak. Thus, the Raman scattering caused by the optical fiber in the Raman probe must be eliminated. For that purpose, it is known to deposit a thin film on the edge surface of the optical fiber by evaporation to thereby form an interference filter. To the tip of the exciting fiber, a band-pass filter is secured with an adhesive in order to eliminate the Raman scattered light generated from the excitation-light transmitting quartz fiber (see Non-patent Document 3).
[Patent Document 1] JP Patent Publication (Kokai) No. 11-218445 A (1999)
[Patent Document 2] U.S. Pat. No. 5,842,995
[Non-patent Document 1] Appl. Spec. 6,619, 1999